The present invention is directed to the prevention of carbon formation in gas phase reforming catalytic operations at temperatures above about 900.degree. F. Reforming is the conversion of high molecular weight hydrocarbons, such as naphtha and crude oil by reaction with steam to lower molecular weight species, such as methane or the conversion of any hydrocarbon to carbon oxides and hydrogen. A particular example is the reforming of methane to hydrogen and the oxides of carbon. Hydrocracking is a form of reforming which includes the conversion of heavier hydrocarbons to lower molecular species by reaction with hydrogen.
The catalytic reforming of natural gas, refinery gases, liquefied petroleum gases and naphthas is practiced commercially for the production of syngases or "rich" gases which are used for the production of hydrogen, ammonia, methanol and other chemicals. Conventionally, the reforming reaction occurs on a nickel-type catalyst in the presence of steam at temperatures ranging from 900.degree. F. to approximately 1600.degree. F. Excess steam over the stoichiometric quantity required for the reforming reaction is used, not only to achieve a high ddgree of conversion to syngas, but also to assist in the prevention of carbon formation from the syngas produced or from a syngas containing hydrogen and carbon oxides which may be added as reactants in the reforming process.
In U.S. Pat. No. 3,103,423 to Pearce, it is disclosed that the presence of sulfur in an amount up to 10 ppm can be tolerated during the reforming of light distillate hydrocarbons and that as a consequence water as steam can be reduced.
Of the hydrocarbons which may be subject to reforming, the aromatic hydrocarbons, particularly benzene, are the most difficult to reform.
In our prior copending application, it was disclosed that the inclusion of a source of hydrogen as part of the feed and present in an amount sufficient for the stoichiometric conversion of carbon in the hydrocarbons to be reformed to methane enables, in the presence of hydrogen sulfide, a high degree of conversions of the more difficult to reform aromatic hydrocarbons at reduced steam requirements. Hydrogen can be provided as such, as carbon monoxide which reacts with water to yield hydrogen in the presence of the reforming agent, as well as part of a syngas, i.e. a mixture comprising hydrogen and the oxides of carbon.
Reducing steam load results in an increase of thermal efficiency for the process and reduced cost of excess steam recovery and separation as a condensate from the product gas.